我遇到一个问题：虚拟网络设备之间存在意外的路由路径。
让我们创建两个独立的 veth-peer 设备对：
$ sudo ip link add veth0 type veth peer name peer0
$ sudo ip link add veth1 type veth peer name peer1
为 peerX 设备分配地址：
$ sudo ip addr add ab:: dev peer0
$ sudo ip addr add cd:: dev peer1
设置所有设备：
$ sudo ip link set dev veth0 up
$ sudo ip link set dev veth1 up
$ sudo ip link set dev peer1 up
$ sudo ip link set dev peer0 up
检查设备：
$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 02:82:b2:df:b0:58 brd ff:ff:ff:ff:ff:ff
inet 10.0.2.15/24 brd 10.0.2.255 scope global dynamic enp0s3
valid_lft 84429sec preferred_lft 84429sec
inet6 fe80::82:b2ff:fedf:b058/64 scope link
valid_lft forever preferred_lft forever
3: peer0@veth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 6e:8d:c0:7c:02:9c brd ff:ff:ff:ff:ff:ff
inet6 ab::/128 scope global
valid_lft forever preferred_lft forever
inet6 fe80::6c8d:c0ff:fe7c:29c/64 scope link
valid_lft forever preferred_lft forever
4: veth0@peer0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 4e:43:26:75:10:11 brd ff:ff:ff:ff:ff:ff
inet6 fe80::4c43:26ff:fe75:1011/64 scope link
valid_lft forever preferred_lft forever
5: peer1@veth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether ea:8c:82:e6:2e:a9 brd ff:ff:ff:ff:ff:ff
inet6 cd::/128 scope global
valid_lft forever preferred_lft forever
inet6 fe80::e88c:82ff:fee6:2ea9/64 scope link
valid_lft forever preferred_lft forever
6: veth1@peer1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether da:5a:68:b1:e8:43 brd ff:ff:ff:ff:ff:ff
inet6 fe80::d85a:68ff:feb1:e843/64 scope link
valid_lft forever preferred_lft forever
和路线：
$ ip r
default via 10.0.2.2 dev enp0s3 proto dhcp src 10.0.2.15 metric 100
10.0.2.0/24 dev enp0s3 proto kernel scope link src 10.0.2.15
10.0.2.2 dev enp0s3 proto dhcp scope link src 10.0.2.15 metric 100
现在在 UDP 端口 2000 上监听 peer0：
$ nc -u -6 -l ab:: 2000
并通过 peer1 发送数据包：
$ echo -n abc nc -u -6 -s cd:: ab:: 2000
并听nc打印abc！但为什么?peer0和peer1没有任何关联。如果我理解正确的话，监听nc应该绑定到peer0，发送nc应该绑定到peer1。
答案1
peer0 和 peer1 没有以任何方式连接。
它们都是属于系统的接口，因此它们与系统相连。路由发生在系统上。系统将直接在属于自己的地址之间进行通信，而不会将数据包路由到外部，即不通过 veth 接口发送数据包，而是使用其 loopback 接口（dev lo如下所示）：
# ip route get from cd:: to ab::
local ab:: from cd:: dev lo table local proto kernel src ab:: metric 0 pref medium
另外，这里没有太大帮助，但是在显示没有任何 IPv6 值来提示 IPv6 的路由时，-6必须给出，否则它默认为 IPv4。
# ip -6 route
ab:: dev peer0 proto kernel metric 256 pref medium
cd:: dev peer1 proto kernel metric 256 pref medium
fe80::/64 dev peer1 proto kernel metric 256 pref medium
fe80::/64 dev veth1 proto kernel metric 256 pref medium
fe80::/64 dev peer0 proto kernel metric 256 pref medium
fe80::/64 dev veth0 proto kernel metric 256 pref medium
# ip -6 route show table local
local ::1 dev lo proto kernel metric 0 pref medium
local fe80::4c43:26ff:fe75:1011 dev veth0 proto kernel metric 0 pref medium
local fe80::6c8d:c0ff:fe7c:29c dev peer0 proto kernel metric 0 pref medium
local fe80::d85a:68ff:feb1:e843 dev veth1 proto kernel metric 0 pref medium
local fe80::e88c:82ff:fee6:2ea9 dev peer1 proto kernel metric 0 pref medium
multicast ff00::/8 dev veth1 proto kernel metric 256 pref medium
multicast ff00::/8 dev peer1 proto kernel metric 256 pref medium
multicast ff00::/8 dev veth0 proto kernel metric 256 pref medium
multicast ff00::/8 dev peer0 proto kernel metric 256 pref medium